This invention relates generally to electro-luminescent lamp panels and, more particularly, to the recovery of energy stored in these panels that is otherwise dissipated during the discharge cycle of a drive circuit.
Electro-luminescent lamps act as capacitors, electrically. These lamps store energy, as do all capacitors, in the form of an electrical voltage charge. In the normal electro-luminescent lamp driver circuit, this charge is dissipated, and therefore lost, during the discharge cycle of operation.
Electro-luminescent lamp driver circuits are well known in the prior art, exemplary of which are the Supertex HV803 and the Toko TK659XX. A typical one of these circuits is illustrated in FIG. 1. In that circuit, components L1, S0, D1, and C1 constitute a high voltage boost or step-up converter which receives a low voltage (less than 6 volts) and boosts it to between 20 and 100 voltas on the capacitor C1. Components S1, S2, S3, and S4 constitute a an H-bridge circuit that is used to commutate the high DC voltage on capacitor C1 into a high AC voltage across an electro-luminescent lamp capacitor (C lamp) that is about twice the DC voltage on capacitor C1. This AC voltage charges and discharges the capacitor C lamp, with the energy stored in the capacitor C lamp being dissipated in components S3 and S4 of the H-bridge during the discharge cycle.
It would be advantageous to recover this energy, existing in the form of charge at high voltage, from the electro-luminescent lamp capactior C_lamp, and reuse it, thus making the entire electro-luminescent lamp driving system more efficient. Accordingly, the present invention is directed to circuitry required to implement the recovery of this otherwise lost energy, which is significant in the case of large electro-luminescent lamps that are driven to higher voltages.